Platelet factor XIII-A regulates platelet function and promotes clot retraction and stability

Surface-bound FXIII enhances deposition and straightness of fibrin fibers

Cross-linked fibrous networks are central to maintaining the structural integrity and functional relevance of many biological and engineered materials. Fibrin networks are the building blocks of blood clots, mediators of tissue injury and repair, and synthetic wound sealants. Cross-linking of fibrin fibers is catalyzed by the activated form of transglutaminase enzyme FXIIIa, which becomes available in plasma but is also readily presented on the surface of activated platelets and macrophages. The contribution of surface-bound FXIIIa to fibrin structure has not been well understood. In this work, we investigated the role of surface-bound FXIIIa on the formation and structure of fibrin fibers from FXIII-deficient plasma by confining the cross-linking reactions to the surface of microspheres. Quantitative microscopy revealed that cross-linking on FXIIIa-coated surfaces facilitates fibrin deposition following a sigmoidal kinetics, and that these fibers were straighter, longer, and more numerous compared with uncross-linked fibers bound to surfaces coated with anti-fibrin antibody. Our results suggest that, by modifying local fibrin density and structure, surface-bound FXIIIa may play a significant role in the mechanobiology of hemostasis and inflammation.

Transcription factor RUNX1 regulates coagulation factor XIII-A (F13A1): decreased platelet-megakaryocyte F13A1 expression and clot contraction in RUNX1 haplodeficiency

Background

Germline RUNX1 haplodeficiency (RHD) is associated with thrombocytopenia, platelet dysfunction, and predisposition to myeloid malignancies. Platelet expression profiling of an RHD patient showed decreased F13A1, encoding for the A subunit of factor (F)XIII, a transglutaminase that cross-links fibrin and induces clot stabilization. FXIII-A is synthesized by hematopoietic cells, megakaryocytes, and monocytes.

Objectives

To understand RUNX1 regulation of F13A1 expression in platelets/megakaryocytes and the mechanisms and consequences of decreased F13A1 in RHD.

Methods

We performed studies in platelets, human erythroleukemia (HEL) cells, and human CD34+ cell-derived megakaryocytes including on clot contraction in cells following small inhibitor RNA knockdown (KD) of RUNX1 or F13A1.

Results

Platelet F13A1 mRNA and protein were decreased in our index patient and in 2 siblings from an unrelated family with RHD. Platelet-driven clot contraction was decreased in the patient and affected daughter. Promoter studies in HEL cells showed that RUNX1 regulates F13A1 transcription; RUNX1 overexpression increased, and small inhibitor RNA RUNX1 KD reduced F13A1 promoter activity and protein. Following RUNX1 or F13A1 KD, clot contraction by HEL cells was decreased, as were FXIII-A surface expression, myosin light chain phosphorylation, and PAC1 antibody binding upon activation. F13A1 expression and clot contraction were impaired in RUNX1 downregulation in human megakaryocytes.

Conclusion

RUNX1 regulates platelet-megakaryocyte F13A1 expression, which is decreased in RHD, reflecting regulation of a coagulation protein by a hematopoietic transcription factor. Platelet and megakaryocyte clot contraction is decreased in RHD, related to multiple impaired mechanisms including F13A1 expression, myosin phosphorylation, and αIIbβ3 activation.

Measurement of factor XIII for the diagnosis and management of deficiencies: insights from a retrospective review of 10 years of data on consecutive samples and patients

Background

Factor XIII (FXIII) deficiency is a challenge in the diagnosis of rare bleeding disorders with inherited and acquired causes.

Objectives

We evaluated consecutive cases tested for FXIII deficiency for insights on diagnosis.

Methods

With ethics approval, we retrospectively reviewed FXIII tests performed between 2013 and 2023 and local patient records for insights into causes and presentations of FXIII deficiency.

Results

Two thousand one hundred ninety-one samples from 1915 patients (ages: 0-90 years; 38% local) were tested. The FXIII activity (FXIII:Act; Berichrom FXIII, Siemens Healthcare) was low in 14%/9.7% of tested samples/patients. FXIII subunit A antigen (FXIII-A:Ag; Werfen HemosIL FXIII antigen; low in 45% of 251 samples) helped characterize FXIII deficiency severity and identify type 2 deficiencies from acquired FXIII inhibitors. Urea clot solubility tests (18.2% requested without FXIII:Act) were largely noninformative as all abnormal samples (n = 7) had undetectable FXIII-A:Ag levels. Excluding FXIII inhibitor patients, FXIII:Act showed strong correlation with FXIII-A:Ag (R 2 = 0.84, P < .001) and weak correlation with plasma fibrinogen (R 2 = .005, P < .001). Some patients had combined acquired FXIII and fibrinogen deficiencies from consumption or major bleeding. FXIII-deficient and nondeficient patients had similar bleeding except for more umbilical and gastrointestinal bleeding among deficient patients (P < .05). Most FXIII deficiencies were acquired (92%), and although several were autoimmune, most were from consumption, major bleeds, or severe infections or had uncertain significance, with bleeding sometimes attributable to other causes.

Conclusion

Congenital and acquired FXIII deficiency are associated with bleeding. Local practices were changed to ensure that FXIII:Act is used to screen for FXIII deficiency and that deficient patients have FXIII:Act and FXIII-A:Ag quantified and compared.

Transcription Factor RUNX1 Regulates Coagulation Factor XIII-A ( F13A1 ): Decreased Platelet-Megakaryocyte F13A1 Expression and Clot Contraction in RUNX1 Haplodeficiency

Background

Germline RUNX1 haplodeficiency (RHD) is associated with thrombocytopenia, platelet dysfunction and predisposition to myeloid malignancies. Platelet expression profiling of a RHD patient showed decreased F13A1, encoding for the A subunit of factor XIII, a transglutaminase that cross-links fibrin and induces clot stabilization. FXIII-A is synthesized by hematopoietic cells, megakaryocytes and monocytes.

Aims

To understand RUNX1 regulation of F13A1 expression in platelet/megakaryocyte and the mechanisms and consequences of decreased F13A1 in RHD.

Methods

We performed studies in platelets, HEL cells and human CD34+ cell-derived megakaryocytes including on clot contraction in cells following small inhibitor (si)RNA knockdown (KD) of RUNX1 or F13A1 .

Results

Platelet F13A1 mRNA and protein were decreased in our index patient and in two siblings from an unrelated family with RHD. Platelet-driven clot contraction was decreased in the patient and affected daughter. Promoter studies in HEL cells showed that RUNX1 regulates F13A1 transcription; RUNX1 overexpression increased and (si)RNA RUNX1 KD reduced F13A1 promoter activity and protein. Following RUNX1 or F13A1 KD clot contraction by HEL cells was decreased as were FXIII-A surface expression, myosin light chain phosphorylation and PAC1 binding upon activation. F13A1 expression and clot contraction were impaired on RUNX1 downregulation in human megakaryocytes.

Conclusions

RUNX1 regulates platelet-megakaryocyte F13A1 expression, which is decreased in RHD, reflecting regulation of a coagulation protein by a hematopoietic transcription factor. Platelet and megakaryocyte clot contraction is decreased in RHD, related to multiple impaired mechanisms including F13A1 expression, myosin phosphorylation and αII b β 3 activation. Scientific category - Platelets and thrombopoiesis.

Essentials

RUNX1 regulates expression of FXIII-A chain ( F13A1) in megakaryocytes (MK) and platelets. Platelet and MK F13A1 expression and clot contraction are decreased in RUNX1 deficiency. MK clot contraction, myosin phosphorylation and PAC1-binding are impaired in F13A1 deficiency. Defective clot contraction in RHD arises from defects in multiple platelet-MK mechanisms.

Activated platelets retain and protect most of their factor XIII-A cargo from proteolytic activation and degradation

ABSTRACT

Platelet factor XIII-A (FXIII-A) is a major cytoplasmic protein (∼3% of total), representing ∼50% of total circulating FXIII. However, mobilization of FXIII-A during platelet activation is not well defined. To determine mechanisms mediating the retention vs release of platelet FXIII-A, platelets from healthy humans and mice (F13a1-/-, Fga-/-, Plg-/-, Stim1fl/flPf4-Cre, and respective controls) were stimulated with thrombin, convulxin plus thrombin, or calcium ionophore (A23187), in the absence or presence of inhibitors of transglutaminase activity, messenger RNA (mRNA) translation, microtubule rearrangement, calpain, and Rho GTPase. Platelet releasates and pellets were separated by (ultra)centrifugation. FXIII-A was detected by immunoblotting and immunofluorescence microscopy. Even after strong dual agonist (convulxin plus thrombin) stimulation of human platelets, >80% platelet FXIII-A remained associated with the platelet pellet. In contrast, essentially all tissue factor pathway inhibitor, another cytoplasmic protein in platelets, was released to the supernatant. Pellet-associated FXIII-A was not due to de novo synthesis via platelet F13A1 mRNA. The proportion of platelet FXIII-A retained by vs released from activated platelets was partly dependent on STIM1 signaling, microtubule rearrangement, calpain, and RhoA activation but did not depend on the presence of fibrinogen or plasminogen. Immunofluorescence microscopy confirmed the presence of considerable FXIII-A within the activated platelets. Although released FXIII-A was cleaved to FXIII-A∗ and could be degraded by plasmin, platelet-associated FXIII-A remained uncleaved. Retention of substantial platelet-derived FXIII-A by activated platelets and its reduced susceptibility to thrombin- and plasmin-mediated proteolysis suggest platelet FXIII-A is a protected pool with biological role(s) that differs from plasma FXIII.

Integration of clotting and fibrinolysis: central role of platelets and factor XIIIa

PURPOSE

The aim of the present study was to establish the role of platelets and activated factor XIIIa (FXIIIa) in the structuring of the fibrin network as well as to clarify the effect of network compaction on clot lysis.

METHODS

Turbidimetry was used for the one-stage clotting test where platelet-free plasma (PFP) is regarded as single factor-deficient plasma (platelets as lacking factor) and autologous platelet-rich plasma (PRP) as deficiency corrected plasma. Structural features of the developed and subsequently lysed fibrin network, formed under static and flow conditions, were visualized by confocal microscopy.

RESULTS

Thrombin-initiated plasma clotting revealed changes in the shape of the absorption curve, more pronounced in the presence of platelets. These changes correlate with the transformation of the fibrin scaffold during clot maturing. With the combined action of platelets, thrombin and Ca2+, plasma clotting passes through two phases: initial formation of a platelet-fibrin network (first peak in the polymerization curve), and then the compaction of fibrin, driven by FXIIIa (the second peak) which can be further modulate by the contractile action of platelets. These structural changes, mediated by platelets and FXIIIa, have been shown to determine subsequent clot lysis.

CONCLUSIONS

Platelet aggregates serve as organizing centers that determine the distribution of fibrin in clot volume. The openwork structure of the platelet-transformed fibrin provides the necessary prerequisites for its timely lysis. The revealed aspects of the interaction of platelets and FXIIIa, which accompanies the maturation of a fibrin clot, may lead to new approaches in the pharmacological correction of disorders associated with both thrombotic episodes and bleeding tendency.

How Protein Depletion Balances Thrombosis and Bleeding Risk in the Context of Platelet's Activatory and Negative Signaling

Platelets are small cell fragments that play a crucial role in hemostasis, requiring fast response times and fine signaling pathway regulation. For this regulation, platelets require a balance between two pathway types: the activatory and negative signaling pathways. Activatory signaling mediators are positive responses that enhance stimuli initiated by a receptor in the platelet membrane. Negative signaling regulates and controls the responses downstream of the same receptors to roll back or even avoid spontaneous thrombotic events. Several blood-related pathologies can be observed when these processes are unregulated, such as massive bleeding in activatory signaling inhibition or thrombotic events for negative signaling inhibition. The study of each protein and metabolite in isolation does not help to understand the role of the protein or how it can be contrasted; however, understanding the balance between active and negative signaling could help develop effective therapies to prevent thrombotic events and bleeding disorders.

Progress of nanomaterials in the treatment of thrombus

Thrombus has long been the major contributor of death and disability because it can cause adverse effects to varying degrees on the body, resulting in vascular blockage, embolism, heart valve deformation, widespread bleeding, etc. However, clinically, conventional thrombolytic drug treatments have hemorrhagic complication risks and easy to miss the best time of treatment window. Thus, it is an urgent need to investigate newly alternative treatment strategies that can reduce adverse effects and improve treatment effectiveness. Drugs based on nanomaterials act as a new biomedical strategy and promising tools, and have already been investigated for both diagnostic and therapeutic purposes in thrombus therapy. Recent studies have some encouraging progress. In the present review, we primarily concern with the latest developments in the areas of nanomedicines targeting thrombosis therapy. We present the thrombus' formation, characteristics, and biomarkers for diagnosis, overview recent emerging nanomedicine strategies for thrombus therapy, and focus on the future design directions, challenges, and prospects in the nanomedicine application in thrombus therapy.

Fluorescent peptide for detecting factor XIIIa activity and fibrin in whole blood clots forming under flow

Background

During clotting, thrombin generates fibrin monomers and activates plasma-derived transglutaminase factor (F) XIIIa; collagen and thrombin-activated platelets offer thrombin-independent cellular FXIIIa (cFXIIIa) for clotting. Detecting fibrin on collagen and tissue factor surfaces in whole blood clotting typically uses complex reagents like fluorescent fibrinogen or antifibrin antibody.

Objectives

We want to test whether the peptide using the α2- antiplasmin crosslinking mechanism by FXIIIa is a useful tool in both monitoring FXIIIa activity, and visualize and monitor fibrin formation, deposition, and extent of crosslinking within fibrin structures in whole blood clots formed under flow.

Methods

We tested a fluorescent peptide derived from α2-antiplasmin sequence (Ac-GNQEQVSPLTLLKWC-fluorescein) to monitor the location of transglutaminase activity and fibrin during whole blood clotting under microfluidic flow (wall shear rate, 100 s-1).

Results

The peptide rapidly colocated with accumulating fibrin due to transglutaminase activity, confirmed by Phe-Pro-Arg-chloromethylketone inhibiting fibrin and peptide labeling. The FXIIIa inhibitor T101 had no effect on fibrin generation but ablated the labeling of fibrin by the peptide. Similarly, Gly-Pro-Arg-Pro abated fibrin formation and thus strongly attenuated the peptide signal. At arterial wall shear rate (1000 s-1), less fibrin was formed, and consequently, less peptide labeling of fibrin was detected compared with venous conditions. The addition of tissue plasminogen activator caused a reduction of both fibrin and peptide signals. Also, the peptide strongly colocalized with fibrin (but not platelets) in clots from laser-injured mouse cremaster arterioles. For clotting under flow, FXIIIa activity was most likely plasma-derived since a RhoA inhibitor did not block α2-antiplasmin fragment cross-linking to fibrin.

Conclusion

Under flow, the majority of FXIIIa-dependent fibrin labeling with peptide during clotting was distal of thrombin activity. The synthetic peptide provided a strong and sustained labeling of fibrin as it formed under flow.

Integrin-Dependent Transient Density Increase in Detergent-Resistant Membrane Rafts in Platelets Activated by Thrombin

Platelet lipid rafts are critical membrane domains for adhesion, aggregation, and clot retraction. Lipid rafts are isolated as a detergent-resistant membrane fraction via sucrose density gradient centrifugation. The platelet detergent-resistant membrane shifted to a higher density on the sucrose density gradient upon thrombin stimulation. The shift peaked at 1 min and returned to the control level at 60 min. During this time, platelets underwent clot retraction and spreading on a fibronectin-coated glass strip. Thrombin induced the transient tyrosine phosphorylation of several proteins in the detergent-resistant membrane raft fraction and the transient translocation of fibrin and myosin to the detergent-resistant membrane raft fraction. The level of phosphatidylserine (36:1) was increased and the level of phosphatidylserine (38:4) was decreased in the detergent-resistant membrane raft fraction via the thrombin stimulation. Furthermore, Glanzmann's thrombasthenia integrin αIIbβ3-deficient platelets underwent no detergent-resistant membrane shift to a higher density upon thrombin stimulation. As the phosphorylation of the myosin regulatory light chain on Ser19 was at a high level in Glanzmann's thrombasthenia resting platelets, thrombin caused no further phosphorylation of the myosin regulatory light chain on Ser19 or clot retraction. These observations suggest that the fibrin-integrin αIIbβ3-myosin axis and compositional change of phosphatidylserine species may be required for the platelet detergent-resistant membrane shift to a higher density upon stimulation with thrombin.